DE-44′40′613 C1 (Th. Sprig, P. Seitz; “Vorrichtung und Verfahren zur Detektion und Demodulation eines intensitätsmodulierten Strahlungsfeldes”) teaches an image sensor with multiple sensor elements. Each sensor element (pixel) contains one photo-sensitive site. Each sensor element further contains a plurality of storage sites. The image sensor demodulates the incident electromagnetic wave into the different storage sites and thus allows the reconstruction of the incident wave. The invention allows the acquisition of an object distance. A preferred embodiment of this method relies on charge-coupled devices (CCD), as described by A. J. P. Theuwissen in “Solid-State imaging with charge coupled devices”, Kluwer, Dordrecht, 1995. The disadvantage of the use of this pixel architecture having only one photo-sensitive site and a plurality of storage sites can be found in the bad trade-off that was made between optical sensitivity and sampling/demodulation speed.
DE-198′21′974 A1 (R. Schwarte; “Vorrichtung und Verfahren zur Erfassung von Phase und Amplitude elektromagnetischer Wellen”) teaches the architecture of comb-like striped arrangements of the photo-gates and of the accumulation gates. The invention overcomes the speed limitations by using short paths that the photo-generated charge carriers have to travel for arriving at the storage site. The disadvantage of the invention can be found in the fact that each photo-sensitive site delivers only two samples and not at least three, as required at least to determine offset, amplitude and phase of the incident wave, or four samples at the time, as most phase measuring devices do. The invention mainly relates on DE-44′40′613 C1.
EP-1′152′261 A1 (R. Lange, P. Seitz; “Device and Method for Spatially Resolved Photodetection and Demodulation of Modulated Electromagnetic Waves”) describes a method that employs pixels with two physically separated photo-sensitive areas, each of them delivering two samples. The equal distribution of the incoming electro-magnetic waves is ensured by the use of additional micro-optical elements on top. The method allows performing four samples per period simultaneously on each pixel. It yields high-speed sampling rates and still reaches a reasonable sensitivity (fill factor >10%). The drawback of the method is the use of micro-optical elements on images sensor.
GB-2′389′960 A (P. Seitz; “Four-tap demodulation pixel”) describes a new technology for improving the transfer speed of the photo-generated charge carriers to the storage sites. The goal of the invention relies on delivering more constant, lateral electrical fields in the photo-sensitive area. The invention decreases the speed problem, but it is still desirable to have short transfer paths along the photo-generation site to the storage location. The requirement of short transfer paths again limits the possible photo-sensitive size within each pixel and thus limits the sensitivity, namely the fill factor of the pixel.
So far, without using micro-optical elements, there is no device architecture known in the domain of phase/distance measuring full-field imagers that exhibits very high-speed demodulation operation, i.e., short charge carrier transfer paths from the photo-generation site to the storage site, and at the same time high optical sensitivity, i.e., large photo-sensitive sites.